Rapid convergence of access network

ABSTRACT

The present disclosure describes rapid convergence of an Access Network (AN). A VLAN forwarder is allocated to a first Virtual Local Area Network (VLAN) and traffic for the first VLAN is forwarded to and from the AN via the VLAN forwarder. When detecting that the VLAN forwarder satisfies a VLAN reallocation condition, the VLAN forwarder blocks traffic of the first VLAN to and from the AN via the VLAN forwarder, and calculates a characteristic value of the VLAN forwarder. A packet carrying the characteristic value of the VLAN forwarder is transmitted to each neighbor VLAN forwarder such that VLAN reallocation is performed by a VLAN allocator if the characteristic value of the VLAN forwarder is the same as that of each neighbor VLAN forwarder. After receiving information that the VLAN forwarder is reallocated to a second VLAN, the VLAN forwarder allows the traffic of the second VLAN to and from the AN via the VLAN forwarder.

BACKGROUND

A transport network (also known as a provider network) may be used toconnect multiple geographically dispersed access networks (also known ascustomer networks) via a wide area network. An access network (AN) is anetwork, which connects an access device of a host to a core switchingdevice. One example technology for carrying user traffic through atransport network is Transparent Interconnection of Lots of Links(TRILL), which is a Layer 2 (L2) network standard recommended byInternet Engineering Task Force (IETF). TRILL is configured to solvedeficiencies of Spanning Tree Protocol (STP) in a large-scale datacenter. In a TRILL network, a device running a TRILL protocol may bereferred to as a Routing Bridge (RB) device. The RB device may transmita Hello packet periodically, so as to discover and maintain a neighborrelationship with a neighbor RB. Another example is Ethernet VirtualInterconnect (EVI) where a site network may access a public network viaan edge device (ED).

BRIEF DESCRIPTIONS OF THE DRAWINGS

Features of the present disclosure are illustrated by way of examplesand not limited in the following drawings, in which like numeralsindicate like elements:

FIG. 1 is a schematic diagram illustrating an example network, in whichTRILL is used.

FIG. 2 is a schematic diagram illustrating an example network, in whichEthernet Virtual Interconnect (EVI) is used.

FIG. 3 is a flowchart illustrating an example rapid convergence methodof an Access Network (AN) which may be performed by a device capable ofacting as a Virtual Local Area Network (VLAN) forwarder.

FIG. 4 is a flowchart illustrating an example rapid convergence methodof an AN which may be performed by a device capable of acting as a VLANallocator.

FIG. 5 is a schematic diagram of an example device for rapid convergencedevice of an AN.

FIG. 6 is a schematic diagram of example instructions stored in a memoryand executable by a processor of a device for rapid convergence deviceof an AN.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the present disclosure isdescribed by referring to examples. In the following description,numerous specific details are set forth in order to provide a thoroughunderstanding of the present disclosure. It will be readily apparenthowever, that the present disclosure may be practiced without limitationto these specific details. In other instances, some methods andstructures have not been described in detail so as not to unnecessarilyobscure the present disclosure. As used throughout the presentdisclosure, the term “includes” means includes but not limited to, theterm “including” means including but not limited to. The term “based on”means based at least in part on. In addition, the terms “a” and “an” areintended to denote at least one of a particular element.

In an AN (e.g. TRILL access network or EVI site network etc.), a VLANforwarder may be allocated to a VLAN such that all traffic of the VLANis forwarded to and from the AN via the VLAN forwarder. In certaincircumstances such as when the network topology changes, the VLANforwarder may block the traffic of its allocated VLAN for a period oftime to avoid traffic looping. During this period, traffic of the VLANmay be interrupted, thereby affecting the quality and performance of theAN.

The present disclosure describes rapid convergence of an AN. A VLANforwarder is allocated to a first Virtual Local Area Network (VLAN) andtraffic for the first VLAN is forwarded to and from the AN via the VLANforwarder. When detecting that the VLAN forwarder satisfies a VLANreallocation condition, the VLAN forwarder blocks traffic of the firstVLAN to and from the AN via the VLAN forwarder, and calculates acharacteristic value of the VLAN forwarder. A packet carrying thecharacteristic value of the VLAN forwarder is transmitted to eachneighbor VLAN forwarder such that VLAN reallocation is performed by aVLAN allocator if the characteristic value of the VLAN forwarder is thesame as that of each neighbor VLAN forwarder. After receivinginformation that the VLAN forwarder is reallocated to a second VLAN, theVLAN forwarder allows the traffic of the second VLAN to and from the ANvia the VLAN forwarder.

According to the example of the present disclosure, the VLAN forwardercalculates and transmits its characteristic value when VLAN reallocationcondition is satisfied. Based on the characteristic value of the VLANforwarder, VLAN reallocation is performed to facilitate a quickerrecovery from a traffic blocking period. As such, convergence speed ofthe AN may be accelerated and network performance improved.

It will be appreciated that the terms “first” and “second” here aremerely used to represent the VLAN allocated to the VLAN forwarder priorto the reallocation (i.e. “first VLAN”), and after the reallocation(i.e. “second VLAN”) respectively. In practice, the “first VLAN” and“second VLAN” may be the same, different or overlap with each otherdepending on the reallocation. Further, the term “first VLAN” refers tothe VLAN to which the VLAN forwarder is allocated, and may includemultiple VLANs in practice.

In the following, rapid convergence of AN is discussed with reference totwo example technologies, i.e. TRILL in FIG. 1 and EVI in FIG. 2.However, it will be appreciated that any other suitable technology maybe used in place of TRILL and EVI.

FIG. 1 is a schematic diagram illustrating an example network 100, inwhich the same network segment accesses 120 a TRILL network 120 viamulti-homing. The network 100 includes routing bridge devices 110 (i.e.RB1, RB2), and switches 122 (i.e. SW1, SW2, SW3) belonging to the samenetwork segment 120 (i.e. network segment 1). SW1 and SW2 may access theTRILL network 130 via multi-homing. As shown in FIG. 1, SW1 accesses RB1via port P1, SW2 accesses RB1 via port P2, and SW2 accesses RB2 via portP3. RB1 and RB2 are multi-homing devices with ports 112 P1 and P2, andP3 respectively.

To avoid traffic looping, access and egress to the TRILL network 130 forall traffic of each Virtual Local Area Network (VLAN) within the samenetwork segment may employ the same RB and the same port. The port maybe referred to as an Appointed VLAN-x Forwarder (AVF) (“VLAN forwarder”)of the VLAN, where ‘x’ represents an identifier of the VLAN. As shown inFIG. 1, port P1 is the AVF of VLAN100, port P2 is the AVF of VLAN200 andport P3 is the AVF of VLAN400. All RBs within the same network segment120 (that is, each RB accessing the network segment 120) may interactwith each other using a Hello packet etc., such as to elect a DesignatedRB (DRB). Subsequently, the DRB may allocate an AVF for each VLAN of thenetwork segment.

When a root bridge of a network segment located by an AVF changes, or anAVF of VLAN-x changes (the DRB may reallocate a new AVF for VLAN-x thatis different from the current AVF), to avoid traffic looping, thecurrent AVF needs to block traffic of VLAN-x for a period of time, suchas for a default time period of 30 seconds. Within the period, trafficof VLAN-x may not access the TRILL network.

In an EVI site network, similar cases may also occur. FIG. 2 is aschematic diagram illustrating an example EVI network 200. In this case,the AN is in the form of an EVI site network 220.

By adopting EVI technologies, the network 200 may be divided into a CoreNetwork (CN, public network) 230 and site networks (private networks)220. To provide better services, the CN generally provides L2 VirtualPrivate Network (VPN) services. Each site network 220 may access the CN230 via an Edge Device (ED) 210. A Point-to-Point (P2P) channel 232 maybe established between EDs, to implement L2 interconnection. Toguarantee reliability of data transmission between sites 220 and tosimultaneously implement load sharing, multiple EDs 210 may generally beused within a network site 220. The multiple EDs 210 may access the CN230 via multi-homing, which may be referred to as multi-homing EDs 210.The multi-homing EDs 210 may interact with each other using a Hellopacket etc., and elect a Designated ED (DED). The elected DED mayallocate an Appointed Edge Forwarder (AEF) (“VLAN forwarder”) for eachVLAN. The AEF is one of the multiple multi-homing EDs that may enableall local traffic of each VLAN to access the CN 230 via the AEF.

In the example in FIG. 2, the network 200 includes multiple sites 220,i.e site 1, site 2 and site 3. The EDs 210 of sites 1 and 2 arerespectively ED1 and ED2. The EDs 220 of site 3 are ED3 and ED4, whichmay access the CN 230 via multi-homing. ED3 may interact with ED4 usinga Hello packet etc. ED3 and ED4 may elect a DED (which may be ED3, orED4) to allocate an AEF for each VLAN. As shown in FIG. 2, the AEFallocated for VLAN26-VLAN40 is ED3 (see ‘LFV=26-30’ and ‘LFV=30-40’).The AEF allocated for VLAN10-VLAN25 is ED4 (see ‘LFV=20-25’).

After allocating an AEF for VLAN-x, the AEF may carry all traffic ofVLAN-x to access or leave a site (e.g. ED3 for VLAN26-VLAN40). However,the network topology of the site may change, e.g. due to site division,site fusion etc. To avoid traffic looping, the AEF needs to temporarilyblock traffic of a conflicting VLAN. During the period, traffic of theVLAN cannot access the EVI site network.

FIG. 3 is a flowchart 300 illustrating an example rapid convergencemethod of an AN (e.g. TRILL or EVI) where a VLAN forwarder (e.g. AVF orAEF) is allocated to a first VLAN to forward traffic of the first VLANto and from the AN.

At block 310, when detecting that a VLAN forwarder (e.g. port P1 in FIG.1 or ED3 in FIG. 2) satisfies a VLAN reallocation condition, the VLANforwarder (also referred to as the current VLAN forwarder):

-   -   Blocks traffic of the first VLAN (e.g. VLAN100 for P1 or        VLAN25-40 for ED3) to which the VLAN forwarder is allocated        (block 312).    -   Calculates a characteristic value of the VLAN forwarder (block        314).    -   Transmits a packet carrying the characteristic value of the VLAN        forwarder to each neighbour VLAN forwarder (block 316). In        practice, the characteristic value may be carried in a Hello        packet etc.

At block 320, after the VLAN forwarder is reallocated to a second VLAN,the VLAN forwarder allows traffic of the second VLAN to and from the ANvia the VLAN forwarder.

As shown in the examples, the AN may be a TRILL access network 120 (e.g.FIG. 1), or an EVI site network 220 (e.g. FIG. 2).

When the AN is a TRILL access network 120, the AN may access a TRILLnetwork 130 via multiple multi-homing RBs. A VLAN forwarder refers toany port accessing the AN in the multiple RBs 110. Each port in themultiple RBs, which accesses the AN, is a neighbor VLAN forwarder.Taking FIG. 1 as an example, the TRILL access network 130 is networksegment 1. Port P1 accessing network segment 1 in RB1, port P2 accessingnetwork segment 1 in RB1 and port P3 accessing network segment 1 in RB2are VLAN forwarders. P1, P2 and P3 are also neighbor VLAN forwarders.

Traffic of each VLAN in the TRILL access network 130 may access or leavethe TRILL network 120 via a port (see 112 in FIG. 1). Thus, tofacilitate traffic forwarding to and from the TRILL access network 130via the port 112, VLANs are allocated for ports accessing the TRILLaccess network 130 in the multiple multi-homing RBs 110. In particular,for each VLAN, a port 112 is selected from all ports 112 accessing theTRILL access network 130 in the multiple multi-homing RBs 110. Theselected port 112 may be taken as a VLAN forwarder of the VLAN, which isto forward VLAN traffic from the TRILL access network 130 to the TRILLnetwork 120, and to forward VLAN traffic from the TRILL network 120 tothe TRILL access network 130. The selected port 112 may be referred toas the AVF of the VLAN. Each port 112 accessing the TRILL access network130 in the multiple multi-homing RBs 110 may carry the traffic of someVLANs in the TRILL access network, in which case the port 112 isreferred to as the VLAN forwarder of its allocated VLANs. VLANreallocation may be triggered when VLAN configuration of any portchanges. In addition, each port 112 accessing the TRILL access network130 may also receive a Spanning Tree Protocol (STP) packet from theTRILL access network 130. The STP packet may carry root bridge listinformation of the TRILL network 120. The VLAN reallocation may also betriggered when the root bridge in the TRILL access network 130 changes.

When the AN is the EVI site network 220 (see FIG. 2 again), the AN mayaccess the CN (public network) 230 via multiple multi-homing EDs 210. Inthis case, the VLAN forwarder refers to an ED 210 within an EVI site220. The multiple EDs 210 (e.g. ED3 and ED4 in FIG. 2) are neighbor VLANforwarders.

In the EVI site network 220, to avoid traffic looping, traffic of eachVLAN may access or leave the public network 230 via one of the multiplemulti-homing EDs 210. Thus, VLANs are allocated for the multiplemulti-homing EDs to forward traffic to and from the EVI site network220. An ED (e.g. ED3) is selected from multiple multi-homing EDs (e.g.ED3 and ED4) as a VLAN forwarder of a VLAN (e.g. VLAN26-VLAN40), whichis to forward traffic of the VLAN from the EVI site network 220 to thepublic network 230, and forward traffic of the VLAN from the publicnetwork 230 to the EVI site network 220. In example implementations, theselected ED 210 may be the AEF of the VLAN, in which case the VLAN maybe referred to as an active VLAN of the selected ED 210. Each ED 210 inthe multiple multi-homing EDs may carry traffic of some VLANs in the EVIsite network 220, in which case ED 210 is referred to as the VLANforwarder of those VLANs. VLAN reallocation may be triggered when theVLAN configuration (or, configuration of an extended VLAN) of any ED 210changes. In addition, the multiple multi-homing EDs 210 may also receivean STP packet from the EVI site network 220. The STP packet may carryroot bridge list information of the EVI site network 220. The VLANreallocation may also be triggered when the root bridge of the EVI sitenetwork 220 changes.

Thus, it can be seen from the above examples that regardless of whetherthe AN is a TRILL access network 120 or EVI site network 220, the VLANreallocation conditions are generally the same. Thus, in one example,the VLAN forwarder may determine whether the VLAN forwarder satisfies acondition to activate or trigger VLAN reallocation as follows. When theVLAN configuration of the current VLAN forwarder changes, the currentVLAN forwarder determines that it has satisfied a VLAN reallocationcondition. Alternatively, after the current VLAN forwarder receives anSTP packet from the AN, and the root bridge list carried in the STPpacket is not consistent with root bridge list recorded by the currentVLAN forwarder, determine that the current VLAN forwarder satisfies theVLAN reallocation condition. Meanwhile, the recorded root bridge list isupdated according to the STP packet.

When detecting that the VLAN forwarder satisfies the VLAN reallocationcondition, the VLAN forwarder blocks traffic of all its allocated VLANsto access or leave the AN via the VLAN forwarder, and interact with allof its neighbor VLAN forwarders using a packet, which may be a Hellopacket etc.

For example, after detecting that the current VLAN forwarder (e.g. P1 orED3) satisfies the VLAN reallocation condition, the current VLANforwarder may transmit a Hello packet carrying the characteristic valueof the current VLAN forwarder to all of its neighbor VLAN forwarders(e.g. P1 transmits to P2 and P3, or ED3 to ED4). Similarly, the currentVLAN forwarder may also receive a Hello packet transmitted by itsneighbor VLAN forwarder, which carries the characteristic value of thatneighbor VLAN forwarder (e.g. P1 receives from P2 and P3, or ED3 fromED4).

After receiving the Hello packet transmitted by the neighbor VLANforwarder (e.g. P2 and P3 or ED4), the current VLAN forwarder (e.g. P1or ED3) may update its characteristic value according to the Hellopacket, and compare its characteristic value with that carried in thereceived Hello packet. If the characteristic value of current VLANforwarder is different from the characteristic value carried in thereceived Hello packet, it means that topologies are inconsistent. If thecurrent VLAN forwarder (e.g. P1 or ED3) has already blocked the trafficof all of the VLANs to access or leave the AN via the current VLANforwarder, the blocking state needs to be continuously maintained.Otherwise, if the current VLAN forwarder has not blocked the traffic ofall of the VLANs to access or leave the AN via current VLAN forwarder,it will do so.

In the example shown in FIG. 3, the packet carrying the characteristicvalue of the VLAN forwarder at block 316 may further carry feature orcharacteristic information of the VLAN forwarder transmitting thepacket.

The characteristic value of the current VLAN forwarder (e.g. P1 or ED3)may be calculated or updated as follows.

-   -   Calculate a local abstract corresponding to the current VLAN        forwarder according to the feature information of the current        VLAN forwarder.    -   Calculate a neighbor abstract corresponding to the neighbor VLAN        forwarder according to the recorded feature information of each        neighbor VLAN forwarder.    -   Calculate the characteristic value of the current VLAN        forwarder, according to the local abstract corresponding to the        current VLAN forwarder and the neighbor abstract corresponding        to each neighbor VLAN forwarder.

When the AN is a TRILL access network 120 (see FIG. 1), the featureinformation of the VLAN forwarder (e.g. P1 or ED3) may include a portnumber of the VLAN forwarder, a system identifier of an RB on which theVLAN forwarder is located, an allowed VLAN list of the VLAN forwarder(i.e. a list of VLANs for which access is allowed by the VLANforwarder), and a root bridge list recorded by the VLAN forwarder.

In this case, the local abstract corresponding to current VLAN forwardermay be calculated according to the feature information of current VLANforwarder as follows.

-   -   Employ a predetermined abstract calculation algorithm to perform        a calculation based on the port number of current VLAN        forwarder, the system identifier of the RB located by current        VLAN forwarder, the allowed VLAN list of the current VLAN        forwarder, and the root bridge list recorded by current VLAN        forwarder.    -   Take a result of the calculation as the local abstract        corresponding to current VLAN forwarder.

In one example, the neighbor abstract corresponding to the neighbor VLANforwarder may be calculated according to the recorded featureinformation of each neighbor VLAN forwarder as follows.

-   -   Employ a predetermined abstract calculation algorithm to perform        a calculation based on the port number of the neighbor VLAN        forwarder, the system identifier of the RB located by the        neighbor VLAN forwarder, the allowed VLAN list of the neighbor        VLAN forwarder, and the root bridge list recorded by the        neighbor VLAN forwarder.    -   Take a result of the abstract calculation as the neighbor        abstract corresponding to the neighbor VLAN forwarder.

When the AN is an EVI site network 220 (see FIG. 2), the featureinformation of the VLAN forwarder may include a port number of the VLANforwarder, a system identifier of an ED located by the VLAN forwarder,an allowed VLAN list of the VLAN forwarder, and a root bridge listrecorded by the VLAN forwarder.

In one example, the local abstract corresponding to current VLANforwarder may be calculated according to the feature information ofcurrent VLAN forwarder as follows.

-   -   Employ a predetermined abstract calculation algorithm to perform        a calculation based on the port number of the current VLAN        forwarder, the system identifier of the ED located by the        current VLAN forwarder, the allowed VLAN list of current VLAN        forwarder, and the root bridge list recorded by current VLAN        forwarder.    -   Take a result of the abstract calculation as the local abstract        corresponding to current VLAN forwarder.

In one example, the neighbor abstract may be calculated as follows.

-   -   Employ a predetermined abstract calculation algorithm to perform        a calculation based on the port number of the neighbor VLAN        forwarder, the system identifier of the ED located by the        neighbor VLAN forwarder, the allowed VLAN list of the neighbor        VLAN forwarder, and the root bridge list recorded by the        neighbor VLAN forwarder.    -   Take a result of the abstract calculation as the neighbor        abstract corresponding to the neighbor VLAN forwarder.

In the example shown in FIG. 3, any suitable algorithm may be used. Forexample, the predetermined abstract calculation algorithm is MD5algorithm.

In one example, the characteristic value of current VLAN forwarder maybe calculated according to the local abstract corresponding to currentVLAN forwarder and the neighbor abstract corresponding to each neighborVLAN forwarder as follows.

-   -   Perform a summing operation on the local abstract and the        neighbor abstract.    -   Take a result of the summing operation as the characteristic        value of current VLAN forwarder.

FIG. 4 shows an example VLAN reallocation process performed by a VLANallocator, which may be the current VLAN forwarder (e.g. P1 or ED3)itself or a different VLAN forwarder (e.g. P3 or ED4). A VLAN allocatormay be elected from all the neighbor VLAN forwarders. For example, thecurrent VLAN forwarder (e.g. P1 or ED3) may be elected as a VLANallocator. A different VLAN forwarder may also be elected.

At block 410, the VLAN allocator receives a packet carrying acharacteristic value of a VLAN forwarder.

At block 420, after receiving a packet carrying a characteristic valueof a neighbor VLAN forwarder (the packet is transmitted by each neighborVLAN forwarder), the VLAN allocator may record the characteristic valueof the neighbor VLAN forwarder.

At block 430, when the characteristic value of current VLAN forwarder isthe same as the recorded characteristic value of each neighbor VLANforwarder, VLAN reallocation is performed, i.e. the VLAN allocatorreallocates the VLAN forwarder for each VLAN in the AN.

At block 440, the VLAN allocator sends the VLAN forwarder aboutinformation of a VLAN (also referred to as the “second VLAN” at block320 in FIG. 3) allocated for each VLAN forwarder.

In practice, a VLAN allocator may be elected from multiple VLANforwarders at block 410. When allocating VLANs, the VLAN allocator mayexecute VLAN allocation operations.

When the AN is a TRILL access network 120, a DRB may be elected frommultiple multi-homing RBs 110. A main port 112 may be elected by the DRBfrom all of the ports 112 accessing the AN in the DRB. In one example,the main port 112 may be used as the VLAN allocator in charge ofexecuting VLAN allocation operations. The main port 112 maysimultaneously possess functions of VLAN forwarder and VLAN allocator.

When the AN is a EVI site network 220, a DED may be elected from themultiple multi-homing EDs 210. Take the DED as the VLAN allocator incharge of executing VLAN allocation operations. The DED maysimultaneously possess functions of VLAN forwarder (that is, ED) andVLAN allocator (that is, DED).

When a VLAN forwarder is elected as a VLAN allocator, after receivingthe Hello packet transmitted by each neighbor VLAN forwarder, inaddition to updating the characteristic value of the VLAN allocator, theVLAN allocator may also record the characteristic value of the neighborVLAN forwarder. If the characteristic value of the VLAN allocator is thesame as the characteristic value of each neighbor VLAN forwarder, thismeans there is no topology conflict in the AN. The VLAN reallocation maybe executed. When a VLAN forwarder is elected as the VLAN allocator, theelected VLAN forwarder may possess functions of VLAN forwarder and VLANallocator.

After receiving the Hello packet carrying the characteristic value ofthe neighbor VLAN forwarder transmitted by each neighbor VLAN forwarder,the current VLAN forwarder records the feature information about theneighbor VLAN forwarder carried in the Hello packet, before updating thecharacteristic value of current VLAN forwarder.

VLAN allocation performed by the VLAN allocator may be different forwith different ANs. In the TRILL access network, any suitable AVFallocation method may be employed. In the EVI site network, any suitableAEF allocation method (which may be referred to as an active VLANallocation method) may be employed.

After performing the VLAN reallocation, the VLAN allocator then informsa VLAN forwarder of a VLAN allocated (“second VLAN” for each VLANforwarder, to enable the VLAN forwarder to receive a packet from ortransmit a packet to the VLAN allocated for the VLAN forwarder. Inaddition, when informing the VLAN forwarder about the information of theVLAN allocated for each VLAN forwarder, the VLAN allocator may alsoinform the VLAN forwarder about the characteristic value of the VLANallocator.

Referring to block 320 in FIG. 3 again, the current VLAN forwarder mayreceive the information of the VLAN allocated for current VLAN forwarderfrom the VLAN allocator, and allow the traffic of the VLAN allocated forcurrent VLAN forwarder to and from the AN.

At block 320, after receiving the information of the VLAN allocated forthe VLAN forwarder, which is informed by the VLAN allocator, the VLANforwarder may remove previous blocking state (that blocks traffic of allVLANs to access or leave the AN via the VLAN forwarder), and allow thetraffic of all VLANs allocated for the VLAN forwarder. In addition, wheninformed by the VLAN allocator of the VLAN allocated for current VLANforwarder, the current VLAN forwarder may further receive thecharacteristic value from the VLAN allocator, so as to compare thecharacteristic value of current VLAN forwarder with that received fromthe VLAN allocator. In this case, the current VLAN forwarder may confirmonce again whether a topology conflict exists in the AN. When thecharacteristic value of current VLAN forwarder is the same as thecharacteristic value informed by the VLAN allocator, it means that thereis no topology conflict in the AN. The current VLAN forwarder may allowtraffic of all VLANs allocated for current VLAN forwarder. When thecharacteristic value of the current VLAN forwarder is different from thecharacteristic value informed by the VLAN allocator, it means that thetopology conflict still exists in the AN. In this case, the current VLANforwarder continuously blocks traffic of all VLANs to access or leavethe AN via current VLAN forwarder.

Here, when the AN is the TRILL access network 130, after receiving theinformation of the VLAN allocated by the VLAN allocator for the VLANforwarder, the VLAN forwarder may become the AVF of all VLANs allocatedfor the VLAN forwarder. When the AN is the EVI site network, afterreceiving the information of the VLAN allocated by the VLAN allocatorfor the VLAN forwarder, the VLAN forwarder may become the AEF of all ofthe VLANs allocated for the VLAN forwarder.

The present disclosure also provides a device for rapid convergence ofan AN. Examples will be provided below with reference to FIG. 5 and FIG.6.

FIG. 5 is a schematic diagram of an example device 500 for rapidconvergence of an AN. The device 500 may include memory or storage 520,and a processor 510 in communication with storage 520. The processor 510is to implement rapid convergence of an AN as explained above withreference to FIG. 1 to FIG. 4. In one example, the device 500 is capableof acting as a VLAN forwarder that is allocated to a first VLAN toforward traffic of the first VLAN to and from the AN and comprises aprocessor to (see also FIG. 3):

when detecting that the VLAN forwarder satisfies a VLAN reallocationcondition, block traffic of the first VLAN to and from the AccessNetwork via the VLAN forwarder, calculate a characteristic value of theVLAN forwarder, and transmit a packet carrying the characteristic valueof the VLAN forwarder to each neighbor VLAN forwarder such that VLANreallocation is performed by a VLAN allocator if the characteristicvalue of the VLAN forwarder is the same as that of each neighbor VLANforwarder; and

after receiving information that the VLAN forwarder is reallocated to asecond VLAN, allow the traffic of the second VLAN to and from the AN viathe VLAN forwarder.

The memory or storage 520 may store a characteristic value calculated bythe VLAN forwarder or a neighbour VLAN forwarder. The memory 520 mayalso store instructions 524 executable by the processor 510 for rapidconvergence of the AN. One example of the instructions 524 is shown inFIG. 6, which may include detecting instruction 610, receivinginstruction 620, first controlling instruction 630, and transmittinginstruction 650. It should be understood that although the instructions610 to 650 may be combined or divided in any suitable way, and notlimited to the examples shown in FIG. 6.

In one example, the rapid convergence device may be capable of acting asa VLAN forwarder. In this case, the detecting instruction 610 is todetect whether the device satisfies a VLAN reallocation condition.Receiving instruction 620 is to receive a packet carrying acharacteristic value of a neighbor VLAN forwarder, which is transmittedby each neighbor VLAN forwarder. Receiving instruction 620 is further toreceive information of a VLAN allocated for current VLAN forwarder froma VLAN allocator. In one example, the packet may be a Hello packet. Itshould be noted that, the packet is not limited to the Hello packet inpractice.

When detecting that the device satisfies the VLAN reallocationcondition, according to detecting instruction 610, the first controllinginstruction 630 is to block traffic of all VLANs (also referred to as“first VLAN”) to access or leave an AN via current VLAN forwarder,calculate a characteristic value of current VLAN forwarder, and executetransmitting instruction 650 to transmit a packet carrying thecharacteristic value of current VLAN forwarder to all neighbor VLANforwarders. After receiving VLAN reallocation information of the currentVLAN forwarder from the VLAN allocator according to receivinginstruction 620, the first controlling instruction 630 is further toallow the traffic of all the VLANs (referred to as “second VLAN”)allocated for current VLAN forwarder.

In one example, the device 500 may be capable as acting as a VLANallocator when elected as one. In this case, the memory 520 may furtherstore a second controlling instruction 640. After receiving a packetcarrying the characteristic value of a neighbor VLAN forwarder accordingto receiving instruction 620, the packet being transmitted by eachneighbor VLAN forwarder, the second controlling instruction 640 isfurther to record the characteristic value of the neighbor VLANforwarder. If the characteristic value of the device (i.e. acting as aVLAN allocator) is the same as the recorded characteristic value of eachneighbor VLAN forwarder, the second controlling instruction 640 isfurther to reallocate a VLAN forwarder for each VLAN in the AN, and toexecute transmitting instruction 650 to inform a VLAN forwarder aboutinformation of a VLAN allocated (“second VLAN”) for each VLAN forwarder.

After receiving the packet carrying the characteristic value of theneighbor VLAN forwarder according to the receiving instruction 620, thefirst controlling instruction 630 is further to update thecharacteristic value of current VLAN forwarder. When the updatedcharacteristic value of current VLAN forwarder is different from thecharacteristic value of the neighbor VLAN forwarder carried in thepacket, the first controlling instruction 630 is to block the traffic ofall VLANs (“first VLAN”) to access or leave the AN via current VLANforwarder.

In the above example device, the receiving instruction 620 executable byprocessor 42 and stored in memory 520, is further to receive an STPpacket from the AN.

When detecting whether the device satisfies the VLAN reallocationcondition, detecting instruction 610 is to detect whether VLANconfiguration of current VLAN forwarder changes, and when detecting theVLAN configuration of current VLAN forwarder changes, to determine thatthe device satisfies the VLAN reallocation condition.

Alternatively, when receiving the STP packet from the AN according toreceiving instruction 620, and the root bridge list carried in the STPpacket is not consistent with the root bridge list recorded by thecurrent VLAN forwarder, detecting instruction 610 is to update therecorded root bridge list according to the STP packet, and determinethat the device satisfies the VLAN reallocation condition.

In the above example device, when the AN is a TRILL access network (e.g.see FIG. 1), the AN may access the TRILL network via multiplemulti-homing RBs. The device may be any one of the ports accessing theAN in the multiple RBs. Each port accessing the AN in the multiple RBsis a neighbor VLAN forwarder. The VLAN allocator is a main port electedby a DRB from all ports accessing the AN in the DRB, in which the DRB iselected from the multiple RBs.

In another example, when the AN is an EVI site network (e.g. FIG. 2),the AN may access a public network via multiple multi-homing EDs. Thedevice may be one of the multiple EDs. The multiple EDs are neighborVLAN forwarders. The VLAN allocator may be a DED elected from themultiple EDs.

When the AN is a TRILL access network, the packet may further carryfeature information of a VLAN forwarder, which transmits the Hellopacket. The feature information of the VLAN forwarder may include a portnumber of the VLAN forwarder, a system identifier of an RB located bythe VLAN forwarder, an allowed VLAN list of the VLAN forwarder, and aroot bridge list recorded by the VLAN forwarder.

After receiving the packet carrying the characteristic value of theneighbor VLAN forwarder from each neighbor VLAN forwarder, the firstcontrolling instruction 630 is further to record the feature informationof the neighbor VLAN forwarder carried in the packet, before updatingthe characteristic value of current VLAN forwarder.

When calculating or updating the characteristic value of current VLANforwarder, the first controlling instruction 630 is further to:

-   -   calculate the local abstract corresponding to current VLAN        forwarder according to the feature information of current VLAN        forwarder;    -   calculate the neighbor abstract corresponding to the neighbor        VLAN forwarder according to the recorded feature information of        each neighbor VLAN forwarder; and    -   calculate the characteristic value of current VLAN forwarder        according to the local abstract corresponding to current VLAN        forwarder and the neighbor abstract corresponding to each        neighbor VLAN forwarder.

When calculating the local abstract, the first controlling instruction630 is further to employ a predetermined abstract calculation algorithmto perform a calculation based on the port number of current VLANforwarder, the system identifier of the RB (i.e. device) located bycurrent VLAN forwarder, the allowed VLAN list of current VLAN forwarder,and the root bridge list recorded by current VLAN forwarder, and take aresult of the calculation as the local abstract corresponding to currentVLAN forwarder.

When calculating the neighbor abstract, the first controllinginstruction 630 is further to employ a predetermined abstractcalculation algorithm to perform a calculation based on the port numberof the neighbor VLAN forwarder, the system identifier of the RB locatedby the neighbor VLAN forwarder, the allowed VLAN list of the neighborVLAN forwarder, and the root bridge list recorded by the neighbor VLANforwarder, and then take a result of the calculation as the neighborabstract corresponding to the neighbor VLAN forwarder.

Similarly, when the AN is an EVI site network, the packet may furthercarry feature information of a VLAN forwarder, which transmits thepacket. The feature information of the VLAN forwarder may include a portnumber of the VLAN forwarder, a system identifier of an ED (i.e. device)located by the VLAN forwarder, an allowed VLAN list of the VLANforwarder, and a root bridge list recorded by the VLAN forwarder.

After receiving the packet carrying the characteristic value of theneighbor VLAN forwarder from each neighbor VLAN forwarder, the firstcontrolling instruction 630 is further to record the feature informationof the neighbor VLAN forwarder carried in the packet, before indicatingto update the characteristic value of current VLAN forwarder.

When calculating or updating the characteristic value of current VLANforwarder, the first controlling instruction 630 is further to calculatea local abstract corresponding to current VLAN forwarder, according tothe feature information of current VLAN forwarder, calculate a neighborabstract corresponding to a neighbor VLAN forwarder, according to therecorded feature information of each neighbor VLAN forwarder, andcalculate the characteristic value of current VLAN forwarder, accordingto the local abstract corresponding to current VLAN forwarder and theneighbor abstract corresponding to each neighbor VLAN forwarder.

When calculating the local abstract, the first controlling instruction630 is further to employ a predetermined abstract algorithm to perform acalculation based on the port number of current VLAN forwarder, thesystem identifier of the ED located by current VLAN forwarder, theallowed VLAN list of current VLAN forwarder, and the root bridge listrecorded by current VLAN forwarder, and take a result of the calculationas the local abstract corresponding to current VLAN forwarder.

When calculating the neighbor abstract, the first controllinginstruction 630 is further to employ a predetermined abstractcalculation algorithm to perform a calculation based on the port numberof the neighbor VLAN forwarder, the system identifier of the ED locatedby the neighbor VLAN forwarder, the allowed VLAN list of the neighborVLAN forwarder, and the root bridge list recorded by the neighbor VLANforwarder, and take a result of the calculation as the neighbor abstractcorresponding to the neighbor VLAN forwarder.

The foregoing predetermined abstract calculation algorithm is MD5algorithm. When calculating the characteristic value of current VLANforwarder according to the local abstract corresponding to current VLANforwarder and the neighbor abstract corresponding to each neighbor VLANforwarder, the first controlling instruction 630 is further to perform asumming operation on the local abstract and the neighbor abstract, andtake a result of the summing operation as the characteristic value ofcurrent VLAN forwarder.

Under the circumstances that the above device is elected as the VLANallocator, when executing transmitting instruction 650, so as to informa VLAN forwarder about information of a VLAN allocated for each VLANforwarder, the second controlling instruction 640 is further to informthe VLAN forwarder about the characteristic value of current VLANforwarder.

Under the circumstances that the above device is the VLAN forwarder,when receiving the information of the VLAN allocated for the VLANforwarder from the VLAN allocator, the receiving instruction 620 isfurther to receive the characteristic value informed by the VLANallocator.

Before allowing the traffic of all of the VLANs allocated for the VLANforwarder, the first controlling instruction 630 is further todetermine, whether the characteristic value received from the VLANallocator according to receiving instruction 620 is the same as thecharacteristic value of the VLAN forwarder. When the characteristicvalue received according to receiving instruction 620 is the same as thecharacteristic value of the VLAN forwarder, the first controllinginstruction 630 is to allow the traffic of all of the VLANs allocatedfor the VLAN forwarder. When the characteristic value received accordingto receiving instruction 620 is different from the characteristic valueof current VLAN forwarder, the first controlling instruction 630 is tocontinuously block the traffic of all of the VLANs to access or leavethe AN via the VLAN forwarder.

Alternatively or additionally, the example network device 500 in FIG. 5may be capable of acting as a VLAN forwarder. In one example, theprocessor 510 is to:

receive a packet carrying a characteristic value of the VLAN forwarder,wherein the VLAN forwarder is allocated to a first VLAN and traffic forthe first VLAN is forwarded to and from the AN via the VLAN forwarder;

perform VLAN reallocation if the characteristic value of the VLANforwarder is the same as a characteristic value of each neighbor VLANforwarder; and

send information that the VLAN forwarder is reallocated to a second VLANto the VLAN forwarder.

The methods, processes and functional units described herein may beimplemented by hardware (including hardware logic circuitry), softwareor firmware or a combination thereof. The term ‘processor’ is to beinterpreted broadly to include a processing unit, ASIC, logic unit, orprogrammable gate array etc. The processes, methods and functional unitsmay all be performed by the one or more processors 510; reference inthis disclosure or the claims to a ‘processor’ should thus beinterpreted to mean ‘one or more processors’.

Although one network interface device 540 is shown in FIG. 5, processesperformed by the network interface device 540 may be split amongmultiple network interface devices (not shown for simplicity). As such,reference in this disclosure to a ‘network interface device’ should beinterpreted to mean ‘one or more network interface devices”.

Further, the processes, methods and functional units described in thisdisclosure may be implemented in the form of a computer softwareproduct. The computer software product is stored in a storage medium andcomprises a plurality of instructions for making a processor toimplement the methods recited in the examples of the present disclosure.

The figures are only illustrations of an example, wherein the units orprocedure shown in the figures are not necessarily essential forimplementing the present disclosure. Those skilled in the art willunderstand that the units in the device in the example can be arrangedin the device in the examples as described, or can be alternativelylocated in one or more devices different from that in the examples. Theunits in the examples described can be combined into one module orfurther divided into a plurality of sub-units.

Although the flowcharts described show a specific order of execution,the order of execution may differ from that which is depicted. Forexample, the order of execution of two or more blocks may be changedrelative to the order shown. Also, two or more blocks shown insuccession may be executed concurrently or with partial concurrence. Allsuch variations are within the scope of the present disclosure.

What has been described and illustrated herein are examples of thedisclosure along with some variations. The terms, descriptions andfigures used herein are set forth by way of illustration only and arenot meant as limitations. Many variations are possible within the scopeof the disclosure, which is intended to be defined by the followingclaims—and their equivalents—in which all terms are meant in theirbroadest reasonable sense unless otherwise indicated.

1. A method for rapid convergence of an Access Network (AN), wherein aVLAN forwarder is allocated to a first Virtual Local Area Network (VLAN)and traffic for the first VLAN is forwarded to and from the AN via theVLAN forwarder, the method comprising the VLAN forwarder: when detectingthat the VLAN forwarder satisfies a VLAN reallocation condition:blocking traffic of the first VLAN to and from the AN via the VLANforwarder, calculating a characteristic value of the VLAN forwarder, andtransmitting a packet carrying the characteristic value of the VLANforwarder to each neighbor VLAN forwarder such that VLAN reallocation isperformed by a VLAN allocator if the characteristic value of the VLANforwarder is the same as that of each neighbor VLAN forwarder; and afterreceiving information that the VLAN forwarder is reallocated to a secondVLAN, allowing the traffic of the second VLAN to and from the AN via theVLAN forwarder.
 2. The method according to claim 1, further comprising:receiving a characteristic value of a neighbor VLAN forwarder, updating,by the VLAN forwarder, the characteristic value of the VLAN forwarder;if the updated characteristic value of the VLAN forwarder is differentfrom the characteristic value of the neighbor VLAN forwarder, blocking,by the VLAN forwarder, the traffic of the second VLAN to and from the ANvia the VLAN forwarder.
 3. The method according to claim 2, whereindetecting by the VLAN forwarder whether the VLAN forwarder satisfies theVLAN reallocation condition comprises: when a VLAN configuration of theVLAN forwarder changes, determining that the VLAN forwarder satisfiesthe VLAN reallocation condition; or, after receiving by the VLANforwarder a Spanning Tree Protocol (STP) packet from the AN carrying aroot bridge list that is not consistent with another root bridge listrecorded by the VLAN forwarder, determining that the VLAN forwardersatisfies the VLAN reallocation condition according to the recorded rootbridge list which is updated based on the STP packet.
 4. The methodaccording to claim 3, wherein the AN is a Transparent Interconnection ofLots of Links (TRILL) access network, which accesses a TRILL network viamultiple multi-homing Routing Bridges (RBs); the VLAN forwarder is anyport of all ports accessing the AN in the multiple RBs, each portaccessing the AN in the multiple RBs is a neighbor VLAN forwarder; andthe VLAN allocator is a main port elected as a Designated RB (DRB) fromall ports accessing the AN in the DRB, wherein the DRB is elected fromthe multiple RBs.
 5. The method according to claim 3, wherein the AN isan Ethernet Virtual Interconnect (EVI) site network, which accesses apublic network via multiple multi-homing Edge Devices (EDs); the VLANforwarder is any ED of the multiple EDs, and the multiple EDs areneighbor VLAN forwarders; and the VLAN allocator is a Designated ED(DED) elected from the multiple EDs.
 6. The method according to claim 3,wherein the packet carrying characteristic value of the VLAN forwarderfurther comprises feature information of a VLAN forwarder transmittingthe packet, and the feature information of the VLAN forwarder comprises:a port number of the VLAN forwarder, a system identifier of a devicelocated by the VLAN forwarder, an allowed VLAN list of the VLANforwarder, and a root bridge list recorded by the VLAN forwarder; afterreceiving a packet carrying the characteristic value of a neighbor VLANforwarder transmitted by each neighbor VLAN forwarder, recording, by theVLAN forwarder, the feature information of the neighbor VLAN forwardercarried in the packet, before updating the characteristic value of theVLAN forwarder; wherein calculating or updating the characteristic valueof the VLAN forwarder comprises: calculating a local abstractcorresponding to the VLAN forwarder according to the feature informationof the VLAN forwarder; calculating a neighbor abstract corresponding tothe neighbor VLAN forwarder according to the recorded featureinformation of each neighbor VLAN forwarder; and calculating thecharacteristic value of the VLAN forwarder according to the localabstract corresponding to the VLAN forwarder and the neighbor abstractcorresponding to each neighbor VLAN forwarder.
 7. The method accordingto claim 6, wherein: calculating the local abstract comprises employinga predetermined abstract calculation algorithm to perform a calculationbased on the port number of the VLAN forwarder, the system identifier ofthe device located by the VLAN forwarder, the allowed VLAN list of theVLAN forwarder, and the root bridge list recorded by the VLAN forwarder,and taking a result of the calculation as the local abstractcorresponding to the VLAN forwarder; calculating the neighbor abstractcomprises employing a predetermined abstract calculation algorithm toperform a calculation based on a port number of the neighbor VLANforwarder, a system identifier of a device located by the neighbor VLANforwarder, an allowed VLAN list of the neighbor VLAN forwarder, and aroot bridge list recorded by the neighbor VLAN forwarder, and taking aresult of the calculation as the neighbor abstract corresponding to theneighbor VLAN forwarder.
 8. The method according to claim 7, wherein thepredetermined abstract calculation algorithm is MD5 algorithm; and thecharacteristic value of the VLAN forwarder is calculated by performing asumming operation on the local abstract corresponding to the VLANforwarder and the neighbor abstract corresponding to each neighbor VLANforwarder, and taking a result of the summing operation as thecharacteristic value of the VLAN forwarder.
 9. The method according toany of claim 1, wherein the VLAN forwarder is also the VLAN allocator,and when informing the VLAN forwarder of the second VLAN, the methodfurther comprises: informing, by the VLAN allocator, the VLAN forwarderabout the characteristic value of the VLAN allocator; when receiving theinformation of the second VLAN from the VLAN allocator, receiving, bythe VLAN forwarder, the characteristic value of the VLAN allocator; andbefore allowing the traffic of the second VLAN the method furthercomprises: determining, by the VLAN forwarder, whether thecharacteristic value of the VLAN allocator is the same as thecharacteristic value of the VLAN forwarder; if the characteristic valueof the VLAN allocator is the same as the characteristic value of theVLAN forwarder, allowing the traffic of the second VLAN; otherwise,continuing to block the traffic of to access or leave the AN via theVLAN forwarder.
 10. A method for rapid convergence of an Access Network(AN), wherein a VLAN allocator and a VLAN forwarder are neighbor VLANforwarders, the VLAN forwarder is allocated to a first Virtual LocalArea Network (VLAN) and traffic for the first VLAN is forwarded to andfrom the AN via the VLAN forwarder, and the method comprises the VLANallocator: receiving a packet carrying a characteristic value of theVLAN forwarder; performing VLAN reallocation if the characteristic valueof the VLAN forwarder is the same as a characteristic value of eachneighbor VLAN forwarder; and sending information that the VLAN forwarderis reallocated to a second VLAN to the VLAN forwarder.
 11. A device forrapid convergence device of an Access Network (AN), wherein the deviceis capable of acting as a VLAN forwarder that is allocated to a firstVirtual Local Area Network (VLAN) to forward traffic of the first VLANto and from the AN and comprises a processor to: when detecting that theVLAN forwarder satisfies a VLAN reallocation condition: block traffic ofthe first VLAN to and from the AN via the VLAN forwarder, calculate acharacteristic value of the VLAN forwarder, and transmit a packetcarrying the characteristic value of the VLAN forwarder to each neighborVLAN forwarder such that VLAN reallocation is performed by a VLANallocator if the characteristic value of the VLAN forwarder is the sameas that of each neighbor VLAN forwarder; and after receiving informationthat the VLAN forwarder is reallocated to a second VLAN, allow thetraffic of the second VLAN to and from the AN via the VLAN forwarder.12. The device according to claim 11, wherein the device is capable ofacting as a VLAN allocator and the processor is further to: whenreceiving a packet carrying a characteristic value of a neighbor VLANforwarder, record the characteristic value of the neighbor VLANforwarder; calculate a characteristic value of the VLAN allocator; whenthe characteristic value of the VLAN allocator is the same as therecorded characteristic value, reallocate each VLAN forwarder to asecond VLAN, and inform the VLAN forwarder of the second VLANreallocated to the VLAN forwarder.
 13. The device according to claim 12,wherein: the packet carrying characteristic value of the VLAN forwarderfurther comprises feature information of the VLAN forwarder transmittingthe packet, and the feature information of the VLAN forwarder comprises:a port number of the VLAN forwarder, a system identifier of a devicelocated by the VLAN forwarder, an allowed VLAN list of the VLANforwarder, and a root bridge list recorded by the VLAN forwarder; andthe processor is to calculate the characteristic value of the VLANforwarder by: calculating a local abstract corresponding to the VLANforwarder according to the feature information of the VLAN forwarder;calculating a neighbor abstract corresponding to a neighbor VLANforwarder according to recorded feature information of each neighborVLAN forwarder; and calculating the characteristic value of the VLANforwarder according to the local abstract corresponding to the VLANforwarder and the neighbor abstract corresponding to each neighbor VLANforwarder.
 14. The device according to claim 13, wherein: the processoris to calculate the local abstract using a predetermined abstractcalculation algorithm to perform a calculation based on the port numberof the VLAN forwarder, the system identifier of the device located bythe VLAN forwarder, the allowed VLAN list of the VLAN forwarder, and theroot bridge list recorded by the VLAN forwarder, and taking a result ofthe calculation as the local abstract corresponding to the VLANforwarder; and the processor is to calculate the neighbor abstract usinga predetermined abstract calculation algorithm to perform a calculationbased on a port number of the neighbor VLAN forwarder, a systemidentifier of a device located by the neighbor VLAN forwarder, anallowed VLAN list of the neighbor VLAN forwarder, and a root bridge listrecorded by the neighbor VLAN forwarder, and taking a result of thecalculation as the neighbor abstract corresponding to the neighbor VLANforwarder.
 15. The device according to claim 14, wherein thepredetermined abstract calculation algorithm is MD5 algorithm; and theprocessor is to calculate the characteristic value of the VLAN forwarderby performing a summing operation on the local abstract and the neighborabstract and taking a result of the summing operation as thecharacteristic value of the VLAN forwarder.